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If child domain controller is down but obvious access to child domain mailboxes cannot be accessed.<br />
Since associated users with those child domain mailboxes remains with child domain only, if child DC is down, authentication will not happens<br />
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You need to keep at least two domain controllers in child domain with global catalog enabled in same active directory site as Exchange servers to avoid this situation
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If child domain controller is down but obvious access to child domain mailboxes cannot be accessed.
Since associated users with those child domain mailboxes remains with child domain only, if child DC is down, authentication will not happens

You need to keep at least two domain controllers in child domain with global catalog enabled in same active directory site as Exchange servers to avoid this situation

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So, as I understand, 2 domain controllers have to be located in child domain, and the DC in parent domain should be global catalog server, right? &nbsp;But what about if the link between parent and child domains is down?
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So, as I understand, 2 domain controllers have to be located in child domain, and the DC in parent domain should be global catalog server, right?  But what about if the link between parent and child domains is down?

mohammad naji

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Thanks for your help, that was a perfect. Answer to the question,
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Thanks for your help, that was a perfect. Answer to the question,

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Global catalog server cannot see the objects from child domains, so they cannot access their mailboxes if the child domains controller is down, &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;note that the organization has one exchange 2016 server in parent domain only
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Global catalog server cannot see the objects from child domains, so they cannot access their mailboxes if the child domains controller is down,                                  note that the organization has one exchange 2016 server in parent domain only

Exchange server 2016 and child domains

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.

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Email Servers

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